Thermal stability of ionic liquids (ILs) is of great significance for their applications in dissolving cellulose at elevated temperature. A novel ionic liquid, 1-allyl-3-methylimidazolium chloride ([Amim]Cl), was found to be a powerful solvent for cellulose. However, the study about long-term isothermal stability, thermal decomposition mechanism and decomposition products of [Amim]Cl are scarce. Herein, we studied the thermal stability and degradation mechanism of [Amim]Cl using isothermal thermogravimetric analysis (TGA) experiments and density functional theory (DFT) calculations. The weight loss of [Amim]Cl at 100 C under air atmosphere within 15 days was only 1.9% and [Amim]Cl after long-term heating also had dissolving capability of cellulose, indicating that [Amim]Cl has high thermal stability and can be long-term used at the dissolving temperature of cellulose. Both TGA experiments and DFT calculations revealed [Amim]Cl decomposed along two channels and the main pyrolysis products of the proposed mechanisms were detected using thermogravimetric technique coupled with mass spectrometry (TGA-MS). (C) 2010 Elsevier B.V. All rights reserved.